A microphone array device including a plurality of sound-receiving units such as condenser microphones which convert received acoustic sounds into sound signals to output the sound signals and which performs various sound processing operations based on the sound signals outputted from the sound-receiving units is developed. The microphone array device may be configured to perform a delay-and-sum process which synchronously adds the sound signals outputted from the sound-receiving units to relatively emphasize a target sound more greatly than noise (improve SNR (Signal to Noise Ratio)). The microphone array device may also be configured to suppress noise by a synchronous subtracting process which synchronizes the sound signals with each other to subtract the other sound signal from one sound signal so as to form a dead space with reference to a noise sound (for example, see Yutaka Kaneda, “Applications of digital filters to microphone systems”, The Journal of the Acoustical Society of Japan 45(2), pp. 125-128, 1989).
As in the delay-and-sum process, the synchronous subtracting process, or the like, a microphone array process performed by a microphone array device is a process depending on a status such as a positional relationship between both a plurality of sound-receiving units and a target sound source and an arrangement of a plurality of sound-receiving units. The positional relationship between both the sound-receiving units and the target sound source includes, for example, a positional relationship obtained when the plurality of sound-receiving units are arranged in a direction perpendicular to a direction to the target sound source, a positional relationship obtained when the plurality of sound-receiving units are arranged on a straight line in a direction to the target sound source, and the like. The arrangement of the plurality of sound-receiving units includes distances between the plurality of sound-receiving units, holes to the sound-receiving units, and the like.
More specifically, in the microphone array process, when a status such as a positional relationship between a sound-receiving unit and a target sound source or an arrangement of the plurality of sound-receiving units changes, various processes or parameters used in the various processes needs be sequentially switched.
A recent foldable mobile phone is configured to be capable of being used (telephone call or communication) in a plurality of usage patterns such as a normal style in an unfolded state or a viewer style in which a display screen faces outside (surface) in folding. In most foldable mobile phones, a first housing provided with a display screen and a second housing provided with operation buttons are connected to each other through a hinge portion, and a loud speaker is provided on an end portion opposing a connection portion to the hinge portion of the first housing. Therefore, in such a mobile phone, one microphone is frequently mounted near the hinge portion to prevent the microphone in the viewer style from being excessively close to the loud speaker.
In the mobile phone in which a microphone is arranged near the hinge portion, a position of user's (speaker's) mouth is separated from a position of the microphone, in use in the normal style or in use in the viewer style, an SNR of speech sound decreases, and speech quality is deteriorated. For this reason, a noise suppressing process such as a microphone array process which increases an SNR needs be performed.
As described above, in the microphone array process, when a using state (usage pattern) of a mobile phone is changed, various processes or parameters used in various processes need be switched. Therefore, when the microphone array process is configured to be performed in all of the usage patterns such as the normal style and the viewer style, microphone array processing units corresponding to the usage patterns may be independently prepared, and the microphone array processing units which are operated depending on the usage patterns may be switched.
FIG. 24 is a block diagram showing a configuration of a conventional noise suppressing device. The conventional noise suppressing device includes a first sound input unit 101, a second sound input unit 102, a sensor 103, a housing state determining unit 104, a sound input/output switching unit 105, switches 106, 107, and 110, a first microphone array processing unit 108, a second microphone array processing unit 109, and the like.
Each of the first sound input unit 101 and the second sound input unit 102 includes a microphone and an analog/digital converter (hereinafter referred to as an A/D converter). The first sound input unit 101 and the second sound input unit 102 receive sounds through the microphones, convert the received sounds into time-series analog electric signals, amplify the electric signals through the amplifiers, convert the amplified electric signals into digital sound signals by the A/D converter, and then transmit the digital sound signals to the switches 106 and 107, respectively.
When a noise suppressing device is arranged in, for example, a foldable mobile phone, the sensor 103 is a sensor attached to a hinge portion of the mobile phone. The sensor 103 detects a state of the hinge portion depending on whether the mobile phone is in a normal style (unfolded state) or a viewer style (folded state) and transmits a detection result to the housing state determining unit 104. The housing state determining unit 104 determines whether the mobile phone is in the normal style or the viewer style based on the detection result acquired from the sensor 103, and transmits the determination result to the sound input/output switching unit 105.
The sound input/output switching unit 105 controls switching of the switches 106, 107, and 110 based on the determination result acquired from the housing state determining unit 104. For example, the sound input/output switching unit 105 controls switching of the switches 106 and 107 such that the sound signals from the first sound input unit 101 and the second sound input unit 102 are inputted from the first microphone array processing unit 108 when the determination result acquired from the housing state determining unit 104 is the normal style. At this time, the sound input/output switching unit 105 controls switching of the switch 110 such that the sound signal from the first microphone array processing unit 108 is output externally.
On the other hand, when the determination result acquired from the housing state determining unit 104 is the viewer style, the sound input/output switching unit 105 control switching of the switches 106 and 107 to output sound signals from the first sound input unit 101 and the second sound input unit 102 to the second microphone array processing unit 109. At this time, the sound input/output switching unit 105 controls switching of the switch 110 to externally output a sound signal from the second microphone array processing unit 109.
The first microphone array processing unit 108 and the second microphone array processing unit 109 acquire sound signals outputted from the switches 106 and 107 and perform a microphone array process such as a delay-and-sum process or a synchronous subtracting process based on the acquired sound signals. The first microphone array processing unit 108 performs the microphone array process performed when the mobile phone is used in the normal style, and the second microphone array processing unit 109 performs a microphone array process performed when the mobile phone is used in the viewer style.
With such a configuration, the noise suppressing device may perform a microphone array process depending on a usage pattern of the mobile phone (normal style and viewer style). Noise is appropriately suppressed by the processes depending on the usage patterns to improve sound quality.
Moreover, when the noise suppressing device is arranged in a video camcorder, proposed is a configuration in which a directivity and a recording level of a zoom microphone mounted on the video camcorder are controlled in conjunction with zoom information of the camera (see, for example, Japanese Unexamined Patent Publication No. 2002-204493).
The noise suppressing device including the above configuration switches microphone array processing units to be operated when the usage patterns of the mobile phone are changed. The microphone array processing unit controlled to start operating starts an estimating process of various pieces of information used in the microphone array process from the point of time and start a microphone array process based on the estimated information. Therefore, until appropriate information used for a microphone array process is estimated, the microphone array process based on inappropriate information (for example, preset initial information) is performed. For this reason, the noise suppressing process operates unstably. In particular, when the usage patterns are switched in use of the mobile phone (telephone call), uncomfortable sound processed by the unstable operation is disadvantageously sent to the intended party.